Methods of forming electrically conductive plugs and method of forming resistance variable elements

ABSTRACT

A method of forming an electrically conductive plug includes providing an opening within electrically insulative material over a node location on a substrate. An electrically conductive material is formed within the opening and elevationally over the insulative material. Some of the conductive material is removed effective to recess an outermost surface of the conductive material to from about 100 Angstroms to about 200 Angstroms from an outermost surface of the insulative material after said removing of some of the conductive material. After removing some of the conductive material, remaining volume of the opening over the conductive material is overfilled with an electrically conductive metal material different from that of the conductive material. The metal material is polished effective to form an electrically conductive plug within the opening comprising the conductive material and the metal material. Other aspects and implementations are contemplated.

TECHNICAL FIELD

This invention relates to methods of forming electrically conductiveplugs, and to methods of forming resistance variable elements.

BACKGROUND OF THE INVENTION

Recently, resistance variable memory elements, which includeProgrammable Conductive Random Access Memory (PCRAM), have beeninvestigated for suitability as semi-volatile and non-volatile randomaccess memory devices. A typical PCRAM device is disclosed in U.S. Pat.No. 6,348,365 to Moore and Gilton. In typical PCRAM devices, conductivematerial, such as silver, is incorporated into chalcogenide material.The resistance of the chalcogenide material can be programmed to stablehigher resistance and lower resistance states. The unprogrammed PCRAMdevice is normally in a high resistance state. A write operationprograms the PCRAM device to a lower resistance state by applying avoltage potential across the chalcogenide material.

The programmed lower resistance state can remain intact for anindefinite period, typically ranging from hours to weeks, after thevoltage potentials are removed. The PCRAM device can be returned to itshigher resistance state by applying a reverse voltage potential of aboutthe same order of magnitude as used to write the element to the lowerresistance state. Again, the higher resistance state is maintained in asemi-volatile manner once the voltage potential is removed. In this way,such a device can function as a resistance variable memory elementhaving two resistance states, which can define two logic states.

A PCRAM device can incorporate a chalcogenide glass, for examplecomprising germanium selenide (Ge_(x)Se_(100-x)). The germanium selenideglass may also incorporate silver (Ag) or silver selenide (Ag₂Se).

The amorphous nature of the chalcogenide glass material used in a PCRAMdevice has a direct bearing on its programming characteristics. Thus,the incorporation of silver into the chalcogenide glass requires precisecontrol of the glass composition and silver concentration so as not tocause the chalcogenide glass to change from the desired amorphous stateto a crystalline state.

Exemplary preferred resistance variable devices are described in U.S.patent application Ser. No. 10/819,315 filed on Apr. 7, 2004, entitled“Layered Resistance Variable Memory Device and Method of Fabrication”,naming Kristy A. Campbell, Jiutao Li, Allen McTeer and John T. Moore asinventors. Certain exemplary preferred embodiments of such applicationdisclose Ag received over GeSe received over Ag₂Se as a composite ofsome of the switchable resistance variable material receivedintermediate a pair of electrodes in a memory device. In certaininstances, however, it may be desirable to form Ag directly on (with“on” in this document meaning in at least some direct physical touchingcontact) Ag₂Se. The preferred manner of depositing silver in thefabrication of such devices is by sputtering,from a silver target.Unfortunately when sputtering silver directly onto a silver selenidesurface, the silver tends to agglomerate providing discontinuous andotherwise less than complete covering of the silver over the Ag₂Se, evenat deposition thicknesses on the magnitude of 2,000 Angstroms. Suchsilver agglomeration can cause subsequent processing problems duringoperation of such a memory cell. Use of a chalcogenide glass layer suchas germanium selenide between the silver layer and the silver selenidetends to prevent such undesired silver agglomeration.

A typical resistance variable element comprises a pair of conductiveelectrodes having the chalcogenide glass material received therebetween.One such manner of forming a first of the conductive electrodes is toprovide an elemental tungsten plug within an opening formed inelectrically insulative material. The plug is typically formed byoverfilling the opening with tungsten, followed by chemically mechanicalpolishing the tungsten back to at least the outermost surface of theinsulative material to form an isolated tungsten plug within theopening. A chalcogenide glass layer is deposited thereover, followed byan outer electrode of the device for example also comprising elementaltungsten. The outer electrode and chalcogenide glass material aretypically patterned to form a desired configuration of an individualresistance variable memory element.

Unfortunately, the formation of the typical elemental tungsten metalplug electrode of such devices by chemical mechanical polishing canproduce less than optimized devices. For example, in some instances thechemical mechanical polishing typically causes the tungsten plugs torecess relative to an outermost surface of the surrounding insulatingmaterial after such polishing from about 40 Angstroms to about 80Angstroms. Further, the tungsten as-deposited typically has one or bothof cracks/crevices and sealed voids (sometimes referred to as“keyholes”). Also, the outermost surface of the tungsten within theopenings after the polishing is significantly roughened, for example toa typical roughness of at least 5.0 nanometers RMS roughness. Any one orcombination of these artifacts can make it difficult to get completefilling of the remaining volume of the openings with the subsequentlydeposited chalcogenide glass material of a resistance variable element,leading to less than optimum devices.

While the invention was motivated in addressing the above-identifiedissues, it is in no way so limited. For example, and by way of exampleonly, the invention has applicability to the fabrication of conductivemetal plugs in electrically insulative material, regardless of whethersuch are incorporated in resistance variable elements. The invention isonly limited by the accompanying claims as literally worded, withoutinterpretative or other limiting reference to the specification, and inaccordance with the doctrine of equivalents.

SUMMARY

The invention comprises methods of forming electrically conductiveplugs, and methods of forming resistance variable elements. In oneimplementation, a method of forming an electrically conductive plugincludes providing an opening within electrically insulative materialover a node location on a substrate. An electrically conductive materialis formed within the opening and elevationally over the insulativematerial. Some of the conductive material is removed effective to recessan outermost surface of the conductive material from about 100 Angstromsto about 200 Angstroms from an outermost surface of the insulativematerial after said removing of some of the conductive material. Afterremoving some of the conductive material, remaining volume of theopening over the conductive material is overfilled with an electricallyconductive metal material different from that of the conductivematerial. The metal material is polished effective to form anelectrically conductive plug within the opening comprising theconductive material and the metal material.

In one implementation, a method of forming electrically conductive plugscomprises providing a plurality of openings within electricallyinsulative material over respective node locations on a substrate. Anelectrically conductive material is formed within the openings andelevationally over the insulative material. Some of the conductivematerial is removed effective to recess an outermost surface of theconductive material from an outermost surface of the insulative materialafter said removing of some of the conductive material. A crevice isreceived in at least some of the openings after the removing of some ofthe conductive material. After removing some of the conductive material,remaining volume of the openings over the conductive material isoverfilled with an electrically conductive metal material different fromthat of the conductive material, and effective to fill the crevices. Themetal material is polished effective to form electrically conductiveplugs within the openings comprising the conductive material and themetal material.

In one implementation, a method of forming an electrically conductiveplug comprises providing an opening within electrically insulativematerial over a node location on a substrate. An electrically conductivematerial is formed within the opening and elevationally over theinsulative material. Some of the conductive material is removedeffective to recess an outermost surface of the conductive material froman outermost surface of the insulative material after said removing ofsome of the conductive material. The conductive material has anoutermost surface first roughness within the opening after said removingof some of the conductive material. After removing some of theconductive material, remaining volume of the opening over the conductivematerial is overfilled with an electrically conductive metal materialdifferent from that of the conductive material. The metal material ispolished effective to form an electrically conductive plug within theopening comprising the conductive material and the metal material. Theelectrically conductive plug has an outermost surface second roughnessafter said metal material-polishing which is less than that of the firstroughness.

In one implementation, a method of forming an electrically conductivemetal plug comprises providing an opening within insulative materialover a node location on a substrate. An elemental metal is providedwithin the opening and elevationally over the insulative material. Theelemental metal is chemically mechanically polished with a firstpolishing pad force against the substrate effective to recess anoutermost surface of the elemental metal from an outermost surface ofthe insulative material after said elemental metal chemical mechanicalpolishing. After chemical mechanical polishing the elemental metal,remaining volume of the opening over the polished elemental metal isoverfilled with an electrically conductive metal material different fromthat of the elemental metal, The electrically conductive metal materialis chemically mechanically polishes with a second polishing forceagainst the substrate which is less than that of the first polishing padforce effective to form an electrically conductive metal plug within theopening comprising the elemental metal and the electrically conductivemetal material.

In certain implementations, the invention includes methods of formingresistance variable elements incorporating any one or combination of theabove implementations.

Other aspects and implementations are contemplated.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described below withreference to the following accompanying drawings.

FIG. 1 is a diagrammatic sectional view of a substrate fragment inprocess in accordance with an aspect of the invention.

FIG. 2 is a view of the FIG. 1 substrate at a processing step subsequentto that depicted by FIG. 1.

FIG. 3 is a view of the FIG. 2 substrate at a processing step subsequentto that depicted by FIG. 2.

FIG. 4 is a view of the FIG. 3 substrate at a processing step subsequentto that depicted by FIG. 3.

FIG. 5 is a view of the FIG. 4 substrate at a processing step subsequentto that depicted by FIG. 4.

FIG. 6 is a diagrammatic representation chemical mechanical polishingcomponents useable in accordance with aspects of the invention.

FIG. 7 is a diagrammatic sectional view of an alternate embodimentsubstrate fragment in process in accordance with an aspect of theinvention.

FIG. 8 is a view of the FIG. 7 substrate at a processing step subsequentto that depicted by FIG. 7.

FIG. 9 is a view of the FIG. 8 substrate at a processing step subsequentto that depicted by FIG. 8.

FIG. 10 is a view of the FIG. 9 substrate at a processing stepsubsequent to that depicted by FIG. 9.

FIG. 11 is a view of the FIG. 10 substrate at a processing stepsubsequent to that depicted by FIG. 10.

FIG. 12 is a view of the FIG. 5 substrate at a processing stepsubsequent to that depicted by FIG. 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This disclosure of the invention is submitted in furtherance of theconstitutional purposes of the U.S. Patent Laws “to promote the progressof science and useful arts” (Article 1, Section 8).

The term “resistance variable memory element” is intended to include anymemory element, including Programmable Conductor Random Access Memory(PCRAM) elements which exhibit a resistance change in response to anapplied voltage.

The term “chalcogenide glass” is intended to include glasses thatcomprise an element from group VIA (or group 16) of the periodic table.Group VIA elements, also referred to as chalcogens, include sulfur (S),selenium (Se), tellurium (Te), polonium (Po), and oxygen (O).

The term “silver” is intended to include not only elemental silver, butalso silver with other trace metals or in various alloy combinationswith other metals as known in the semiconductor industry, as long assuch silver alloy is conductive, and as long as the physical andelectrical properties of the silver remain unchanged.

The term “resistance variable material” is intended to includechalcogenide glasses and chalcogenide glasses comprising a metal, suchas silver or metal ions. For instance, the term “resistance variablematerial” may include silver doped chalcogenide glasses,silver-germanium-selenide glasses, chalcogenide glass comprising asilver selenide layer, and non-doped chalcogenide glass, as well as suchmaterial incorporating metals in addition to or other than silver and/orgermanium.

Exemplary preferred aspects of the invention and methods of formingelectrically conductive metal plugs are initially described withreference to FIGS. 1-5. FIG. 1 depicts a substrate fragment 10,preferably comprising a semiconductor substrate. In the context of thisdocument, the term “semiconductor substrate” or “semiconductivesubstrate” is defined to mean any construction comprising semiconductivematerial, including, but not limited to, bulk semiconductive materialssuch as a semiconductive wafer (either alone or in assemblies comprisingother materials thereon), and semiconductive material layers (eitheralone or in assemblies comprising other materials). The term “substrate”refers to any supporting structure, including, but not limited to, thesemiconductive substrates described above. Substrate fragment 10 isdepicted as comprising a substrate material 12, for example bulkmonocrystalline silicon. In the fabrication of an electricallyconductive plug, such can be considered as comprising some suitable nodelocation 14 with which electrical contact will be made. In the depictedexemplary embodiment, such comprises a conductive diffusion region 16 ofsuitable conductivity doping. Any alternate node location 14 is also ofcourse contemplated. For example, and by way of example only, analternate node location comprises an outermost surface of a conductivepillar received between a pair of transistor gate lines.

An electrically insulative material 18 has been formed over substrate12, and an opening 20 has been provided therein over node location 14.Exemplary preferred electrically insulative materials 18 include dopedand undoped silicon dioxides (i.e., borophosphosilicate glass (BPSG) asa doped example) and silicon nitride, of course including collections ofthese and other materials. Opening 20 can be provided by any suitableexisting or yet-to-be developed manner, with photolithographicprocessing and etch being but one example. Electrically insulativematerial 18 can be considered as having an outermost surface 22 whichmay or may not be planar.

Referring to FIG. 2, a first electrically conductive material 24 isformed within opening 20 and elevationally over insulative material 18.Exemplary preferred materials include elemental-form metals, conductivemetal compounds, and conductively doped semiconductive materials (i.e.,polysilicon). An exemplary preferred elemental-form material istungsten. Elemental-form material might comprise an alloy of elementalmetals. By way of example only, elemental metal alloys might compriseany combination of two or more elemental metals. Conductive material 24can be considered as comprising an outermost surface 21.

Referring to FIG. 3, some of conductive material 24 has been removedeffective to recess outermost surface 21 of conductive material 24 fromoutermost surface 22 of insulative material 18 after such conductivematerial-removing. Insulative material outermost surface 22 might also,of course, be removed whereby it moves inwardly relative to/towards theunderlying substrate material, such as substrate 12. Exemplary mannersof removal include chemical mechanical polishing, chemical etching,resist-etch-back, 100% mechanical polishing, etc. In one exemplaryimplementation, the removing of some of the conductive material iseffective to recess outermost surface 21 thereof to a dimension “A” fromabout 100 Angstroms to about 200 Angstroms from outermost surface 22 ofelectrically insulative material 18 after such conductivematerial-removing. More preferably, dimension “A” is from about 120Angstroms to about 200 Angstroms, and even more preferably from 155Angstroms to 165 Angstroms. Regardless, in one exemplary implementation,outermost surface 21 of conductive material 24 has some first roughnesswithin opening 20 after removing of some of the conductive material. Inone exemplary embodiment, such first roughness is at least 4 nanometersRMS roughness, and perhaps at least 5 nanometers RMS roughness.

The preferred method of removing some of conductive material 24 ischemical mechanical polishing. FIG. 6 diagrammatically, and by way ofexample only, illustrates a chemical mechanical polishing system 100comprising a rotatable polishing pad 104 and a rotatable substratecarrier 102. Substrate 10 is depicted as being received by carrier 102.A slurry emitter 106 is diagrammatically depicted for emitting slurryonto pad 104 to be received intermediate the pad and substrate. Ofcourse, the pad and substrate carrier might rotate in the same ordifferent directions.

In one implementation, elemental metal 24 is chemical mechanicallypolished with a first polishing pad force against substrate 10. Anexemplary first polishing force against substrate 10 is at least 3.0psi, and more preferably at least 3.5 psi. An exemplary polishing slurrycomprises H₂O, a surfactant, silica, and from about 0.8% to about 1.5%H₂O₂ by weight, with 0.9 weight percent being a specific preferredexample. An exemplary commercially available slurry comprising asurfactant, water and silica is W2585 available from The CabotMicroelectronics Corporation of Phoenix, Ariz., and to which thepreferred H₂O₂ is added. An exemplary preferred slurry flow rate rangeis from 75 mL/minute to 200 mL/minute, with 150 mL/minute being aspecific example. An exemplary preferred pad is Model OXP3150 availablefrom Rohm & Haas Electronic Materials of Newark, Del. An exemplarypreferred rotational speed for each of the pad and carrier is from about30 rpm to 90 rpm, more preferably from 50 rpm to 55 rpm for thepolishing pad, and from 70 rpm to 75 rpm for the substrate carrier. Onespecific preferred example (for example for elemental tungsten) is a padrotation speed of 75 rpm, and a substrate carrier rotation speed of 51rpm. An exemplary chemical mechanical polishing system is a MIRRA Systemavailable from Applied Materials of Santa Clara, Calif. Other systems,slurries, materials and operating parameters are also contemplated.

Referring to FIG. 4, and after removing some of conductive material 24,the remaining volume of opening 20 over conductive material 24 isoverfilled with a second electrically conductive metal material 28,which is different from that of conductive material 24. In the contextof this document, “metal material” encompasses any one or combination ofan elemental metal, an alloy of elemental metals, and any conductivemetal compound. By way of example only, exemplary electricallyconductive metal materials comprise conductive metal nitrides, with TiNand WN being but two examples. Alternate exemplary electricallyconductive metal materials might comprise at least one of Cu, Pt, Ti,Ni, Co, Pd, Mo, Zr, Ta, and C in elemental or alloy form. Any otherconductive metal material, including conductive metal compounds, iscontemplated. The conductive material and the electrically conductivemetal material might have or share a common metal element, for examplean elemental or alloy tungsten material 24 and tungsten nitride formaterial 28. Alternately by way of example only, the conductive materialand the electrically conductive metal material might not have or share acommon element, for example a tungsten material 24 and titanium nitridefor material 28.

Referring to FIG. 5, electrically conductive metal material 28 has beenpolished effective to form an electrically conductive plug 30 withinopening 20 comprising conductive material 24 and metal material 28. Inone implementation, electrically conductive plug 30 has an outermostsurface 33 having an outermost surface second roughness after such metalmaterial-polishing which is less than that of the first roughness. Inone implementation, the second roughness is no greater than 2 nanometersRMS roughness, and in one implementation the second roughness is nogreater than 1 nanometer RMS roughness. Outermost surface 33 mightelevationally coincide with outermost surface 22 of electricallyinsulative material 18, might be recessed relatively thereto, or mightbe received elevationally outward thereof. Further and regardless,surface 22 might move inwardly by polishing action thereagainst duringthe polishing of electrically conductive metal material 28.

In one implementation, the manner of polishing material 28 is chemicalmechanical polishing, which may use the same or different compositionpolishing slurry as described above, and which was preferably utilizedin the first preferred chemical mechanical polishing. In one preferredimplementation, the chemical mechanical polishing of electricallyconductive metal material 28 is conducted with a second polishing forceagainst substrate 10 which is less than that of the first polishing padforce. In one example, the second polishing force against the substrateis from 1.0 psi to 2.0 psi, with an exemplary preferred narrower rangebeing from 1.4 psi to 1.6 psi. Other parameters and materials areotherwise preferably as described above with the first embodimentpreferred chemical mechanical polishing.

The invention also, of course, contemplates methods of forming aplurality of electrically conductive plugs. For example, and by way ofexample only, such is described in a preferred exemplary embodiment withrespect to FIGS. 7-11 with respect to a substrate fragment 10 a. Likenumerals from the first-described embodiment have been utilized whereappropriate, with differences being indicated with the suffix “a”, orwith different numerals. FIG. 7 depicts providing a plurality ofopenings 20 and 40 within insulative material 18a over respective nodelocations 14 and 42 on a substrate 12. Node location 42 is depicted ascomprising a conductive diffusion region 44 within material 12, like thefirst embodiment, with materials of composition and methods ofprocessing otherwise being preferably as described above. Other nodelocations are of course contemplated, for example as described above.

Referring to FIG. 8, electrically conductive material 24 a has beenformed within openings 20 and 40, and elevationally over material 18 a.A crevice 45 and a sealed void 47 are depicted as being received withinopening 40 within conductive material 24 a. An exemplary such creviceand void might also form in the above-described first embodiment.Further and regardless, only a single of such crevice and sealed voidmight form within the conductive material with respect to an individualopening in material 18/18 a. Materials and processing for the formationof conductive material 24 a are otherwise preferably as described abovein the first embodiment with respect to material 24.

Referring to FIG. 9, some of conductive material 24 a has been removedeffective to recess an outermost surface 21 a of conductive material 24a from an outermost surface 22 a of insulative material 18 a after suchconductive material-removing. Crevice 45 is received in at least somethe openings after removing some of the elemental metal 24 a, and sealedopening 47 has become a crevice 49. In the depicted exemplary describedembodiment, crevice 45 typically forms upon the deposition of material24 a. However in one aspect, the invention envisions the provision of acrevice 45 within at least some of the openings independent of whethersuch is formed in the initially deposited material or by subsequentprocessing, including for example by the polishing or other partialremoval thereof. Other processing and attributes are otherwise typicallyand preferably as described above. In one implementation, after suchremoving, individual crevices 45 and 49 have respective maximum openwidths which are less than 50% of a minimum width of the respectiveopening in which the crevice is received, more preferably less than 33%,and even more preferably less than 25%.

Referring to FIG. 10 and after removing some of conductive material 24a, the remaining volume of the openings over conductive material 24 a isoverfilled with an electrically conductive metal material 28 a which isdifferent from that of conductive material 24 a, and effective to fillcrevices 45 and 49. Preferred and exemplary materials 28 a are the sameas those described above for material 28 in the above-describedembodiments.

Referring to FIG. 11, electrically conductive metal material 28 a hasbeen polished effective to form electrically conductive plugs 30 and 50within openings 20 and 40, respectively, comprising conductive material24 a and electrically conductive metal material 28 a. Preferred andexemplary manners of polishing are preferably as described above in thefirst-described embodiment.

Aspects of the invention also encompass methods of forming a resistancevariable element utilizing any one or combination of the above-describedtechniques and attributes. For example, FIG. 12 depicts electricallyconductive plug 30 as comprising a first electrode of a resistancevariable element 75. A chalcogenide glass material 60 has been formedover conductive material plug-comprising first electrode 30, and asecond electrode 70 has been formed over chalcogenide glass material 60to form resistance variable element 75. Exemplary materials 60 and 70,by way of example only, are as described above in the backgroundsection.

In compliance with the statute, the invention has been described inlanguage more or less specific as to structural and methodical features.It is to be understood, however, that the invention is not limited tothe specific features shown and described, since the means hereindisclosed comprise preferred forms of putting the invention into effect.The invention is, therefore, claimed in any of its forms ormodifications within the proper scope of the appended claimsappropriately interpreted in accordance with the doctrine ofequivalents.

1-19. (canceled)
 20. A method of forming an electrically conductiveplug, comprising: providing an opening within electrically insulativematerial over a node location on a substrate; forming an electricallyconductive material within the opening and elevationally over theinsulative material; removing some of the conductive material effectiveto recess an outermost surface of the conductive material from anoutermost surface of the insulative material after said removing of someof the conductive material, the conductive material having an outermostsurface first roughness within the opening after said removing of someof the conductive material; after removing some of the conductivematerial, overfilling remaining volume of the opening over theconductive material with an electrically conductive metal materialdifferent from that of the conductive material; and polishing the metalmaterial effective to form an electrically conductive plug within theopening comprising the conductive material and the metal material, theelectrically conductive plug having an outermost surface secondroughness after said metal material-polishing which is less than that ofthe first roughness.
 21. The method of claim 20 wherein the firstroughness is at least 4 nanometers RMS roughness, and the secondroughness is no greater than 2 nanometers RMS roughness.
 22. The methodof claim 21 wherein the first roughness is at least 5 nanometers RMSroughness, and the second roughness is no greater than 1 nanometer RMSroughness. 23-30. (canceled)
 31. The method of claim 20 wherein removingsome of the conductive material is effective to recess the outermostsurface of the conductive material to from about 100 Angstroms to about200 Angstroms from the outermost surface of the insulative materialafter said removing of some of the conductive material.
 32. The methodof claim 31 wherein removing some of the conductive material iseffective to recess the outermost surface of the conductive material tofrom 120 Angstroms to about 200 Angstroms from the outermost surface ofthe insulative material after said removing of some of the conductivematerial.
 33. The method of claim 31 wherein removing some of theconductive material is effective to recess the outermost surface of theconductive material to from 155 Angstroms to about 165 Angstroms fromthe outermost surface of the insulative material after said removing ofsome of the conductive material.
 34. The method of claim 20 wherein theconductive material comprises metal in elemental form.
 35. The method ofclaim 34 wherein the elemental metal comprises tungsten.
 36. The methodof claim 20 wherein the conductive material comprises a conductive metalcompound.
 37. The method of claim 20 wherein the conductive materialcomprises conductively doped semiconductive material.
 38. The method ofclaim 20 wherein the removing of some of the conductive material and thepolishing of the metal material comprise chemical mechanical polishing.39. The method of claim 38 wherein said chemical mechanical polishingsuse the same composition polishing slurry.
 40. The method of claim 20wherein the metal material comprises a metal nitride.
 41. The method ofclaim 40 wherein the metal nitride comprises at least one of TiN and WN.42. The method of claim 41 wherein the conductive material compriseselemental tungsten.
 43. The method of claim 20 wherein the conductivematerial within the opening comprises a crevice after said removing someof the conductive material, the metal material filling the crevice.